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A new UCLA study shows that different parts of the brain are stimulated in reaction to pain depending on gender. The research, which represents the largest gender-comparison study of its kind, focused on people with irritable bowel syndrome (IBS), one of the nation's most common chronic medical conditions. The findings may help develop and target better treatments for IBS and other illnesses.

"We are finding more scientific differences between men and women as we improve research methods and broaden study populations," said study co-author Dr. Emeran Mayer, UCLA professor of bio-behavioral sciences, and medicine, physiology and psychiatry. "This growing base of research will help us develop more effective treatments based on a new criteria: gender."

Dr. Mayer is the director of the new Center for Neurovisceral Sciences & Women's Health (CNS) at UCLA, which conducted the study.

Published in the June 2003 issue of the journal Gastroenterology, the study examined 26 women and 24 men with IBS. UCLA researchers took positron emission tomography (PET) brain scans of patients during mild pain stimuli.

Although researchers found some overlapping areas of brain activation in men and women, several areas of male and female brains reacted differently when given the same pain stimulus. The female brain showed greater activity in limbic regions, which are emotion-based centers. In men, the cognitive regions, or analytical centers, showed greater activity.

"The reason for the two different brain responses may date back to primitive days, when the roles of men and women were more distinct," said study co-author Dr. Bruce Naliboff, UCLA clinical professor of psychiatry and biobehavioral sciences, and co-director of CNS.

According to Naliboff, these gender differences in brain responses to pain may have evolved as part of a more general difference in stress responses between men and women. Men's cognitive areas may be more highly triggered because of the early male role in defending the homestead, where in response to stress and pain, the brain launched a calculated fight-or-flight reaction.

The female limbic regions may be more responsive under threat because of their importance in triggering a nurturing and protecting response for the young, leading to a more emotion-based response in facing pain and stress.

Naliboff noted that both responses have advantages and neither is better. In fact, under conditions of external threat, the different responses may lead to complementary behaviors between men and women.

In addition, researchers found that the anticipation of pain generated the same brain responses from study volunteers as the actual pain stimulus. "The brain is a powerful force in dictating how the body responds to pain and stress," said study co-author Dr. Lin Chang, UCLA associate professor of medicine and co-director of CNS.

The next step, according to Mayer, is to look at how the results of the study may impact treatment for IBS and other disorders. Mayer adds that one current drug for IBS, Lotronex, affects the limbic system and has worked more successfully in women than men.

UCLA's Center for Neurovisceral Sciences and Women's Health studies how the brain, stress and emotions impact the development of disorders that affect mainly women.

Irritable bowel syndrome affects 15 to 20 percent of Americans and causes discomfort in the abdomen, along with diarrhea and/or constipation.

The National Institute of Diabetes and Digestive and Kidney Diseases and the National Institute of Nursing Research, both part of the National Institutes of Health, funded the study.